The present invention relates to a resiliently deformable element made of an elastomeric material having a microcellular structure, which can be used as an end stop in a motor vehicle suspension, in particular a suspension of the Mac Pherson type.
As is known, suspensions of this type substantially comprise a shock absorber the casing of which is pivoted to an axle or a half-shaft of the motor vehicle and the rod of which is pivoted to a suitable part of the motor vehicle body itself; a coil spring, coaxial with the shock absorber, is interposed between this and the body and has a lower end which rests on a suitable shoulder rigidly connected to the casing of the shock absorber and an upper end which rests against a seating of the motor vehicle body. In suspensions of this type a resiliently deformable element is also normally inserted, the functions of which are those of constituting an end stop to the deformation of the suspension and also a true and proper resilient element, at least during a part of the deformation of the supsension itself.
Deformable elements of this type normally have a tubular form and therefore have an axial hole through which passes the rod of the shock absorber an upper end of which is able to engage on a suitable seating in the body and a lower end against which a surface of the casing of the shock absorber comes into contact during operation of the suspension.
It has been found that for a correct operation of suspensions of this type the overall resilient characteristic of the suspension itself, that is to say the variation of the force transmitted through it in dependence of the axial deformation, must, in a first section, be substantially rectilinear and, in a second section, not linear but with a rigidity which increases with an increase in the deformation; it has in fact been found that such variation there is contemporaneously obtained a greater comfort of ride, a better road holding and a more marked resilient return of the suspension.
Since the deformable elements first described, as well as constituting end stops to the deformation of the suspension, constitute true and proper resilient elements along with the springs of the suspension itself, their resilient characteristic (variation of the axial force exerted by them in dependence on their deformation) must be defined in a rigorous manner. It has in fact been found that deformable elements particular suitable for this purpose have a non-linear characteristic substantially comprising a first section of lower rigidity and a second section of higher rigidity than that of the preceding section, separated by a somewhat marked knee. Characteristics of this type can be obtained only with deformable elements having a very complex form; in fact, a deformable element which has been proposed for this purpose has a first part substantially in the form of a sleeve and a second part which extends from the first part and which is shaped in the form of a bellows. In this way the two parts have a differentiated rigidity and, therefore, during a first part of the deformation of the suspension only the second part of the deformable element is active, this having a smaller rigidity, while in the remaining part of the deformation the part with a higher rigidity is active.
Deformable elements of the type described above have various disadvantages.
First of all, because of their complex form, their manufacture is difficult and requires complex and expensive tooling; such deformable elements in fact have numerous overhangs which make their extraction from the forming moulds particularly difficult; also, because of the geometric complexity the time required for their removal from the mould is particularly long.
Finally, the bending forces due to the bellows-type geometry create critical zones which can reduce the resistance to fatigue; in fact, several parts of the deformable element of the above-indicated type work in flexure and therefore, in these parts, rupture by fatigue can easily occur.